Place an oven rack in the upper third of your oven and preheat to 400°F Butter six half-cup ramekins or souffle molds; pour some granulated sugar into each mold, then tilt and turn to coat completely. Tap out any excess sugar. Place molds on a baking sheet.
In a medium saucepan, whisk together flour, 1/3 c sugar and salt. Add about one-third of the milk (3 tbsp) and whisk to make a smooth paste; add the remaining milk and whisk until smooth. Cook over medium heat, whisking frequently until thickened (about the consistency of thin yogurt), about 5 minutes. Off heat, whisk in egg yolks and butter. Return to heat and cook until just a few bubbles form and pop on the surface. Transfer to a large (at least 4 qt) bowl. Stir in lemon zest and candied lemon peel, and let cool at least 15 minutes. Stir in 3 1/2 tbsp lemon juice.
Whip egg whites until frothy (by hand, with a hand-held electric mixer on low, or in a stand mixer with the whip attachment on low). Increase speed to high and gradually add the remaining 1 1/2 tbsp sugar. Continue beating until stiff, shiny peaks form.
Stir 1/4 of the whites into the cooled lemon base, then fold the remaining whites in gently, in two or three doses, folding gently to avoid deflating the whites. (It's okay if a few streaks of unmixed white remain visible.).
Divide the souffle mix evenly amongst the prepared ramekins. Sprinkle the top of each with a thin, even layer of sugar, then with 1/4 tsp of lemon juice. Bake until the tops are lightly browned and the souffles jiggle when nudged, about 10 minute Serve at once.